AppleTV might be improved with an upgraded power cord, but it still uses an internal switching power supply. This is the main limiting factor on these streamer boxes.
If you are willing to look at an alternative to the AppleTV, my recommendation would be to buy a Roku Ultra streamer. Then get an external 12V linear power supply and ask someone to custom make a DC cable with 1.7mm x 4.75mm DC plug for the Roku. That will significantly improve things (both audio as well as video quality).